1. Technical Field of the Invention
The present invention relates to a mobile telecommunications network and, in particular, to a preemption method for optimizing channel resource management within such a network.
2. Description of Related Art
A "radio interface" or "air interface" provides the connection between a particular mobile station traveling within a particular cell area and a base transceiver station (BTS) providing radio coverage for that particular cell area. Within both analog and digital communications systems, the number of frequency channels allocated for effectuating air-interfaces with mobile stations traveling within a particular cell area is fixed. Because of this limitation, mobile service providers often employ a number of channel resource management schemes to better utilize or to manage these valuable radio frequency resources.
One such scheme is to bias the granting of channel requests in congested situations. For instance, depending on the state of channel congestion, a channel request for an outgoing call connection towards a wireline directory number is rejected and a channel is instead made available to an incoming call connection towards a registered mobile station. There are several reasons for such a biasing. First, for an incoming call connection, a registered mobile station (turned on mobile station) is more likely to answer the call than a wireline station. Furthermore, the end-to-end circuit connection has almost already been established in the case of an incoming call connection towards a mobile station. For example, a circuit connection from an originating telecommunications exchange serving the calling party subscriber terminal to a mobile switching center (MSC) serving the called party mobile station has already been established leaving only the last leg of the call connection between the serving BTS and the mobile station to be completed.
Another scheme involves forcefully terminating an established call connection with a low priority and reusing the same resource for a higher priority call. This approach is referred to as preemption and is undesirable given the negative impact on the preempted mobile subscriber. Furthermore, not knowing what has happened to the call, the preempted mobile subscriber is more likely to re-establish the call connection further aggravating the congestion situation within the serving telecommunications network.
Currently within a digital communications system, such as the Global System for Mobile (GSM) communication standard based networks, an increase in call capacity within a particular geographic area can be achieved by deploying a number of different channel rates or schemes. For example, instead of using each time slot or channel within a frame to transport data associated with a call connection at a 13 KBit/s rate, each channel is further divided into two or more sub-channels with a lower data rate to effectuate a larger number of call connections. As an illustration, each time slot or channel is sub-divided into two separate sub-channels, each sub-channel utilizing a half-rate channel scheme for transporting data at a 6 KBit/s rate. As a result, eight time-slots within a Time Division Multiple Access (TDMA) frame, for example, are sub-divided into sixteen half-rate sub-channels to effectuate sixteen call connections.
However, due to a lower digital sampling of subscriber speech, the half-rate channel scheme achieves poorer voice quality than the full-rate channel scheme. Accordingly, unless there exists a demand for high call capacity, service providers typically prefer to assign full-rate channels with associated mobile stations to provide better quality speech connections. However, once a channel is assigned using the full-rate channel scheme and the demand in call capacity subsequently increases to a level where demanded call connections cannot be handled, unless one of the above described preemption or preference methods is utilized, an increase in call capacity cannot be achieved. Moreover, as described above, forcefully terminating an existing call connection or barring an outgoing call connection using one of the above described methods is undesirable and inefficient.
Accordingly, there is a need for a mechanism to better manage or utilize existing channel resources without terminating an established call connection within a mobile telecommunications network.